Apparatus for bending thermoplastic pipes

ABSTRACT

Method of bending thermoplastic pipes involving applying a source of heat to those portions of the pipe which are to be fashioned or shaped, applying a bending force to the pipe and cooling the bent pipe. The steps of the method are undertaken at one and the same location while the pipe is internally supported and has one end secured in a fixed position. Apparatus specifically designed to carry out such a method is also included.

United States Patent 1 Parmann May 20, 1975 1 APPARATUS FOR BENDINGTHERMOPLASTIC PIPES [76] Inventor: Gunnar Parmann, Kongsmyrvn 28b,

5070 Mathopen, Norway [22] Filed: Jan. 4, 1973 [21] Appl. No.: 321,028

[30] Foreign Application Priority Data Jan. 12, 1972 Norway 48/72 [52]U.S. Cl. 425/384; 425/389; 425/392 [51] Int. Cl. B29c 17/02 [58] Fieldof Search 425/384, 387, 389, 392, 425/393, 395, 342, 340, 403, 343;65/108,

[56] References Cited UNITED STATES PATENTS 1,877,628 9/1932 Replogle264/322 X 1,877,629 9/1932 264/92 2,480,774 8/1949 Rosshcim et al264/339 X Jones 425/392 2,998,985 9/1961 Burns CI 8.1.... 264/295 X2,999,272 9/1961 Wamken 425/389, 3,184,796 5/1965 Southcott et al.425/384 3,753,635 8/1973 Barnett 425/162 Primary ExaminerRobert D.Baldwin Assistant Examiner-David B. Smith Attorney, Agent, orFirm-Kenyon & Kenyon Reilly Carr & Chapin 57 ABSTRACT Method of bendingthermoplastic pipes involving applying a source of heat to thoseportions of the pipe which are to be fashioned or shaped, applying abending force to the pipe and cooling the bent pipe. The steps of themethod are undertaken at one and the samelocation while the pipe isinternally supported and has one end secured in a fixed position.Apparatus specifically designed to carry out such a method is alsoincluded.

23 Claims, 6 Drawing Figures PATENTED MY 2 0 SHEET 1 [1F 3 PATENTED MAY2 01975 SHEET 3 OF 3 APPARATUS FOR BENDING THERMOPLASTIC PIPES Thisinvention relates to a apparatus of bending thermoplastic pipes bysubjecting the pipe to bending forces in a heated condition in order,thereafter, to cool down the pipe into a finished bent condition, aswell as to apparatus which can be used to achieve this purpose.

With all pure bending of pipes, there generally occurs a distribution ofstress with a tensile stress on the one side portion which is to befashioned with the largest radius of curvature, that is to say having aconvex curvature (stretch side), and with a compressive stress on theother side portion which is to be fashioned with the least radius ofcurvature, that is to say having a concave curvature (compression side).Generally, the tensile stresses have a tendency to flatten out the pipeon the convex side portion, while the compressive stresses have atendency to produce local inward and outward bulging, that is to saycorrugating or folding on the concave side portion.

In order to be able to deform a thermoplastic pipe to a desired bentshape, it is necessary that the pipe be heated to a suitable shaping orfashioning temperature. However, as a result of the heating, thedurability of shape of the pipe is reduced since the annular rigidityand ability of the cross-section of the pipe to absorb compressivestresses is significantly reduced. It is necessary, therefore, duringthe heating of thermoplastic pipes to carry out extra measures so as toavoid folding together of the cross-section of the pipe and so as topreclude the compressive forces from producing corrugations or foldswhen the pipe, in the heated condition, is subjected to bendingstresses.

Hitherto, it has been usual to effect bending of thermoplastic pipes inseveral distinct operations. In a first operation, the pipe is filledwith a filling composition which has often been preheated so that at thesame time the pipe obtains a desired internal reinforcement by thefilling composition, there is also obtained a desired preheating of theinner side of the pipe. In a subsequent second operation the pipe, whichis filled with filling composition, is heated uniformly, in a suitableheating apparatus, from the external side along the whole of the regionof the pipe which is to be bent. In a third operation, the pipe istransferred to a bending jig, where it is bent against an externalmould. During the bending, it has hitherto been necessary to have aconstant visual control and modification of the bending operation, forexample, local after-heating of the pipe in order to avoid corrugationsor folds on the compression side and contraction of the pipecross-section on the stretch side. When the pipe has received thedesired bending, the pipe is cooled in a cautious manner, for example,by means of wet filler or the like so as to be disposed later in a waterbath for further cooling.

The hiterto employed methods for bending thermoplastic pipes have beenrelatively expensive to carry out, the bending being both timeandlabourconsuming as a consequence of performing the manufacture inseveral separate working operations with the necessary vigilance andmodification of the bending operation in each instance so that automaticmanufacture has been more or less impossible to carry out. In thebending of large and heavy pipe dimensions, the manufacture has beenespecially clumsy and uneconomic. When extra filling composition isutilised, there have occurred big problems in being able to support thepipe in a satisfactory manner on transferring the heated pipe from theheating apparatus to the bending apparatus. This applies in particularto large pipes having a diameter of from 255 mm and above.

It is an object of the present invention to provide a method andapparatus for bending thermoplastic pipes in which treatment of the pipebefore, during and after the bending operation can be carried out in aconvenient and simple manner and to a large degree automatically.

According to the present invention a method of bending thermoplasticpipes comprises the steps of (a) applying a source of heat to thoseportions of the pipe which are to be fashioned, (b) applying a bendingforce to said pipe and (c) cooling the fashioned pipe, steps (a), (b)and (0) being carried out at one and the same location while the pipe isinternally supported and one end thereof is held in a fixed position.

Also according to the invention is apparatus for bending thermoplasticpipes capable of functioning as a self-contained unit and comprising (a)heat-transfer means for controllably heating and cooling such a pipe,(b) means for locating one end of the pipe in a fixed positionexternally of said heat-transfer means, and (c) means for internallyreinforcing the pipe and means for applying a bending force theretowhile said pipe is received in said heat-transfer means with said oneend in said fixed position, the heat-transfer means being adapted topivot as the pipe is being bent by actuation of the bendingforce-applying means.

It has been found to be especially convenient to supply the greatestamount of heat to that section of the periphery of the pipe to bestretched to the maximum and to supply a smaller amount of heat to thatsection of the periphery of the pipe to be stretched, if at all, to theminimum.

The heat-transfer means can suitably be in the form of a jacket ofsubstantially U-shaped cross-section adapted to surround, while spacedfrom, the pipe to form internal heat-transfer medium-conveying or guidesurfaces with nozzles fixed at the base of the U-shape for supplyingheat-transfer medium to be directed at the pipe and to be led or guidedby said surfaces to effect the controlled heating and cooling of thepipe. In a preferred construction, the heat-transfer mediumconveyingsurfaces define with the pipe narrow gaps at a transition zoneintermediate one side portion of the pipe facing the nozzles and anotherside portion facing away from the nozzles, said internal surfacesprojecting freely outwards a distance beyond said another side portionto form a whirl chamber immediately adjacent the latter.

The means for locating one end of the pipe can constitute a holder towhich the upper end of the pipe can be secured and from which said pipecan then be freely suspended downwards substantially vertically.Conveniently, the holder can be fixed to an upstanding support columnwith the heat-transfer means pivotally mounted on said holder below theupper end of the pipe. Desirably, an abutment member of preselectedcurvature is mounted on the holder and serves as a stop for one sideportion of the pipe during bending thereof. The apparatus may alsoinclude means for applying direct heat to the internal walls of the pipepivotally mounted on the support column above the holder therebyenabling said means to be swung away from the pipe when not in use.

The means for internally reinforcing the pipe can comprise means forclosing off the freely suspended pipe by insertion in the lower thereofplus filler mate rial, if desired pre-heated, deposited in theclosed-off pipe.

Alternatively, the means for internally reinforcing the pipe cancomprise an inflatable container, optionally weight-loaded, adapted tobe lowered into the pipe and to be inflated to a pressure sufficient tocause said container to abut the pipe so as to provide a reinforcementtherefor while suspended therein and means for lowering and raising saidcontainer into and out of the pipe when said container is in its normaldeflated condition.

By firmly holding the one end of the pipe during heating, bending andcooling, several advantages can be obtained. One of these advantages isthat the manufacture can be effected in a continuous process, that is tosay without dividing up into the hitherto employed, sepa rate workingoperations and without having to transfer from apparatus to apparatus.Another advantage is that by so locating the one end of the pipe, therecan be ensured a better controlled and more precisely performablemanufacture, with the possibility for automatic operation and consistentaction on subsequent pipes during the manufacture. For one thing, onecan act on the pipe with respect to a desired stress and/or compressionloading.

In order to effect the heating or cooling-down with a gaseous medium orif desired a combination of gaseous or liquid medium there is thepossibility of quite simply regulating the flow conditions of the mediumor media so as to achieve a desired differential heating of the twoopposite sides of the pipe, that is to say the stretch side and thecompression side. By directing the medium in the form of a jet directlyagainst the stretch side of the pipe, there can be obtained anespecially intense heating effect on this portion of the side of thepipe. By further regulating the speed of flow of the jet and the heatcontent and/or by a suitable arrangement of the shape of the guidesurfaces projecting freely outwards a distance beyond the pipe, therecan be achieved a desirably controlled heating, not only of the stretchside of the pipe, but also of the compression side of the pipe. Theheating of the compression side of the pipe can be regulated more orless independently of the heating of the stretch side of the pipe byregulating the speed of flow of the jet of medium. By utilising a lowspeed of flow, one can, for example, allow the flow of medium to followthe periphery of the pipe from the stretch side to the compression sideso that there can be obtained a relatively uniform heating of the twoopposite side portions. By utilising a higher flow rate, one can allowthe flow of medium to follow externally arranged guide surfaces soshaped as to lead, thereby, the gas medium positively away from theother side portion (the compression side) so that the latter iscorrespondingly less heated. A specially adjusted heating effect can beobtained on the compression side of the pipe, by producing a desirablystrong whirling effect in the region outside the said other side portionof the pipe (compression side). The heating can, for example, bearranged so that the temperature on the stretched side-forming sideportion lies in a region of from above 150 to 200C, while thetemperature on the oppositely disposed side portion lies in a region offrom 100 up to 150C. Immediately the pipe is finally formed, the heatcontent of the flow of medium can be regulated in a suitable manner froma high heat level to a suitably low heat level, with the correspondingpossibility of adjusting the flow conditions. at the two opposite sideportions according to desire and need.

The described method of heating makes it possible to achievetemperatures in the pipe portions to be bent which correspond to thedesired elongations, as the side portions which are to be streched mostare heated to the highest temperature and the side portions of theopposite side are heated to the lower temperature.

The method of heating makes it possible to obtain a sufficient rigidityon the pipe side portion which is to be formed with a concave curvature,to withstand bulging and buckling as a result of the compressivestresses occurring during bending.

In certain circumstances, especially as regards thinwalled thermoplasticpipes or pipes of thermoplastic materials which are little suited toabsorbing compression forces without bulging or buckling, one can, in asimple manner, as a consequence of the one pipe end being secured, allowthe compression forces which would otherwise occur in the pipe, to beoverlapped by a tensile force. It is preferred, in this connection, thatthe pipe be suspended substantially vertically, preferably in a freedownwardly hanging position, secured at the upper end of the pipe sothat the weight of the pipe and a possible extra weight loading (ortensile loading) on the latter, exerts a tensile loading which overlapsthe compressive stresses otherwise occuring on bending on the pipe sideportion which is to be formed with a concave curvature.

In order that the invention can be more clearly understood, convenientembodiments thereof will now be described, by way of example, withreference to the accompanying drawings in which:

FIG. 1 is a vertical elevation of the apparatus according to theinvention illustrated in a starting position of the bending process,

FIG. 2 is a plan of a portions of the apparatus of FIG.

FIGS. 3 and 4 are horizontal sections of portions of the apparatusillustrating various flow conditions.

FIG. 5 is a vertical elevation of the apparatus of FIG. 1 after thebending process is concluded, and

FIG. 6 is a fragmentary view of an inflatable container in the lower endof a pipe being processed in the heat chamber of the apparatus accordingto the invention.

Referring to the drawings, there is shown a pipe bending apparatuscomprising a horizontal supportforming foot plate 10 and a verticalsupport column 11 for supporting the pipe 12 which is to be bent, in avertical downwardly hanging starting position. At a suitable heightabove the foot plate 10, there is fixed a sleeve-shaped pipe holder 13which is adapted to form an abutment against portions of the uppersocket portion 14 of the pipe and with its upper edge 13a an abutmentfor an annular collar 15 of the pipe socket portion 14. The pipe holder13 is obliquely cut underneath at 13b to permit the bending of the pipe12 from the position illustrated in FIG. 1 to the position illustratedin FIG. 5. The pipe holder 13 is readily displaceable so as to be ableto be adapted to various desired pipe dimensions which are to be bent.

To the respective lower edges of the pipe holder, there is secured aheat chamber 16 pivotably mounted about a horizontal axis 16a at rightangles to the plane of the drawing in FIG. 1. The chamber 16 is providedwith a horizontal top member 17 which defines a seat for the pipe and ahorizontal bottom member 18 which defines a seat for the pipe 12. Thechamber 16 also has vertical side members 19-23 to define a U-shapedjacket. From the central side member 21 (see FIG. 2-4), there divergeobliquely outwards in opposite directions, the side members and 22towards to side members 19 and 23. The lower end of the pipe 12 isreceived in a concave cavity 18a in the shaped end of the bottom member18 of the chamber 16, while the upper end of the pipe is arranged in acorresponding cavity in the inlet shaped end of the top member 17without contacting the latter. Laterally there are formed relativelynarrow gaps 19a and 23a between the pipe 12 and the side members 19 and23. There is formed a chamber 24 between the side members 20, 21, 22,the top member 17, the bottom member 18 and portions of the side members19, 23 together with the one side 12a of the pipe 12.

Directly opposite the side 12a of the pipe, means are fixed in the sidemember 21 for directing at least one flow of heated air transverselyonto and around the pipe. This means includes three compressed airnozzles 25, 26, 27 at a suitable height above each other and in theintermediate spaces between the latter two, means for directing at leastone flow of water transversely of the pipe are used. These latter meansinclude pressure water nozzles 28, 29. It will be understood that it ispossible to arrange less or more nozzles if required. The nozzles -27are adapted to be able to supply compressed air having an individuallyregulatable pressure and/or individually regulatable heat content. Ifdesired, there can be added steam or water directly to the pressureforces. Similarly the pressure water nozzles 28, 29 can be supplied withhot or cold water as required. The water is preferably added compressedair to give a wanted water spray. The nozzles 25-27 and 28, 29 areadapted to emit substantially conical jets of pressure medium asillustrated by the jet lines 27a in FIGS. 3 and 4, having direct impactagainst the one side 12a of the pipe which is to be subjected to anespecially intense heating and cooling.

The pressure medium flows from the chamber 24 further past the pipe inthe gaps 19a and 23a between the pipe 12 and the side members 19 and 23and is conveyed further outwards by means of the side members 19 and 23which are extended a distance past the outwardly directed side portion12b of the pipe 12. In the region between the side members 19 and 23outside the side of the pipe 12b there is formed a whirl chamber 30having an opening to the open air for exhausting the heated air flowpassing away from the pipe.

When working with pipes of larger diameter, it has proved necessary toarrange the guide surface-forming side members 19 and 23 so that theyconverge somewhat thereby limiting the whirl chamber, at the sideportion 12b of the pipe, to a relatively narrow belt reckoned in thelongitudinal direction of the pipe.

The whirl effect in the chamber 30 is dependent upon the rate of flow ofthe pressure medium and the shape of the side members 19 and 23, and byregulating the pressure of the pressure medium and/or the shape of theside members 19 and 23, the whirl effect can be regulated as requiredand thereby the discharging of the pressure medium along the side 12b ofthe pipe can be regulated. By suitable simultaneous regulation of thepressure and heat content of the pressure medium, there can be achieved,as required, smaller or larger temperature differences on the oppositeside portions 12a and 12b of the pipe 12. For example, the pipe sideportion 12a can be heated to a temperature of from above 150 up to 200Cwhile the pipe side portion 12b can be heated to a temperature of fromup to C.

As is evident from FIG. 2, the pipe holder 13 is substantially C-shapedin horizontal section with the opening of the C-shape direction outwardsfrom the plane of the drawing in FIG. 1 so that the pipe 12 can bearranged readily in place sideways in the pipe holder. In order to beable to arrange the pipe simultaneously sideways in place in the chamber16, the side member 23 is, as illustrated in FIG. 2, pivotable about avertical axis 31 relatively to the adjacent side member 22.

To the bottom member 18 of the chamber 16, there is secured a pipesupport member 32. Via a pin 33, the chamber 16 is linkably connected toa piston rod 34 of a compressed air cylinder 35, the opposite end ofwhich is pivotably mounted on a pin 36 in a bracket 37 fixed to the footplate 10. At 38, there are indicated conduits for the pressure mediumwhich is to displace the piston rod between the positions illustrated inFIG. 1 and 5.

To the side portion of the pipe holder directly above .the horizontalpivotal axis of the chamber 16, there is secured a bent pipe supportrail 39 having a curvature which forms a stop for the side 12b of thepipe and ensures that the latter obtains a desired degree of angle asillustrated in FIG. 5.

In the embodiment as illustrated in the drawings, hot air is suppliedinternally to the pipe 12 by arranging a compressed air nozzle 390 withhot air of an air drying apparatus or a similar combined blowing andheating apparatus, just above the upper end of the pipe as shown inFIG. 1. The compressed air nozzle is secured to a support arm 40 whichis pivotable about a vertical axis 41 on the column 11 so that thecompressed air nozzle 39a or the like can be swung to the side as shownin FIG. 5, as required.

A separate rubber container 42 is adapted to be lowered by way of asupport line 43 and a compressed air cylinder 44 into place in the place12. In the illustrated embodiment, the support line extends in aU-shaped path from the compressed air cylinder 44 via gear means (notshown) to a fastening on the rubber container 42. The rubber containercomprises a reinforced bottom portion 42a, a radially expandable sleeveportion 42b and a reinforced top portion 42c which is provided with acompressed air conduit 45. After the rubber container is lowered intoplace in the heated pipe 12, the rubber container is blown up to asuitable pressure so that it forms an internal abutment against the pipeand reinforces the latter in a desired manner. lmmediately the pipe isfinally bent, and cooled, the compressed air is let out of the rubbercontainer 42 and the rubber container can be drawn up again from thepipe and brought into place in the position which is shown in FIG. 1.

Instead of the illustrated compressed air nozzle 39a and the rubbercontainer 42, there can be utilized another form of internalreinforcement of the pipe 12. There can be utilised, for example, arubber container which is introduced from the lower end of the pipe asuitable distance into the pipe to a level below that portion of thepipe which is to be bent. The container can be radially stretched bymeans of compressed air to seal off the lower end of the pipe. Afterthis it can be filled with sand, gravel, metal balls (steel shot) orsimilar filling material M in suitable quantities. The filling materialused can in a manner per se be preheated before it is introduced in thepipe and can impart a suitable quantity of heat to the inner side of thepipe in advance, as well as during, the whole of the bending process,that is to say up to the rubber container is removed from the pipe andthe filling material thereby discharged.

In an instance where the rubber container 42 is used for the internalreinforcement of the pipe, a desired relatively tensile effect can beobtained during bending, produced substantially by the weight of thepipe as a result of the pipe being suspended in a vertical position withsupport at its upper end. A certain increase of the tensile loading canbe achieved by weight loading the rubber container in a suitable manner.On the other hand by using sand, gravel, metal balls or similar materialhaving a relatively large specific gravity, as combined filling materialand weight loading, there can be obtained a desired, especially strong,tensile loading in the pipe.

A strong tensile loading can be advantageous for, for example,thin-walled plastic pipes (which have a small wall thickness and therebyalso a relatively small tensile effect as a result of small weight) orplastic pipes of material which is difficult to shape. By overlappingthe compressive stresses, which would otherwise occur on that side ofthe pipe which is to be fashioned with a concave curvature, with tensilestresses, the folding effects can be avoided which otherwise have atendency to occur on this side portion of the pipe. On the opposite sideportion the filling material, and the reinforcing rubber container, willprevent the tensile stresses occurring during the bending together withthe tensile stresses which are produced by the extra weight loading,from producing folding together of the pipe cross section.

Mode of Operation After a pipe 12 is pushed laterally into place in thepipe holder 13 and the chamber 16, and after the side member 23 of thechamber is swung into place from the position illustrated in FIG. 2 tothe position illustrated in FIG. 1, the pipe 12 is heated internally bya hot compressed air stream which is supplied from the compressed airnozzle 39a. After a suitable time interval, the compressed air supply tothe compressed air nozzle 39a is closed off and the latter is swung tthe side as shown in FIG. 5. The rubber container 42 is thereafterlowered into place in the pipe, blown up with compressed air to asuitable pressure so that there is exerted a definite, moderate pressureagainst the inner walls of the pipe. After this hot compressed air issupplied via the nozzles 25-27 to the chamber 24 with the jets directedmore or less at right angles against the portion 12a of the side of thepipe which is to be fashioned or shaped with the strongest convexcurvature, the jets being deflected laterally along the periphery of thepipe and flowing outwards through the gaps 19a and 23a be tween thechamber 16 and the pipe and being conveyed further outwards along theguide surface-forming side members 19 and 23, past the pipe 12. To beginwith,

there can be utilised a lower pressure on the hot air jets so that thehot air stream flows more or less uniformly along the whole of theperiphery of the pipe as illustrated in FIG. 3, thereby resulting in apreliminary uniform heating of the whole of the periphery of the pipe.To achieve a uniform overlap between the not heated parts of the pipeand the parts to be heated the nozzles 25 and 27 can be adjusted to alower temperature than the nozzle inbetween. Gradually there can beobtained a more intense heating of the side 12a of the pipe which is tobe subjected to the greatest bending, by increasing the pressure of thehot air jet. Such a pressure increase involves increasing the rate offlow of the hot air stream against the side portion 12a and through thegaps 19a and 23a and thereby forcing the flow of hot air in a directionoutwards from the outwardly directed side portion 12b of the pipe alongthe guide surface-forming side members 19 and 23 so that there is formedan increased whirl effect in the chamber 30 as indicated in FIG. 4, anda lower heating of the side portion 12b of the pipe than the sideportion 12a thereof. During the heating period or after the pipe hasobtained the wanted temperatures, the bending is performed with theassistance of the compressed air cylinder.

Immediately the pipe is finally bent to a desired angle with abutmentagainst a desired length of the pipe support rail 39, the cooling of thepipe can be proceeded with. This can be effected gradually and in anaccurate adjusted manner, by utilising suitably tempered cold airstreams instead of the previously utilised hot air streams or by coolingdown the hot air streams by the addition of cold water through separatefine distribution nozzles or, if desired, by the addition of cold waterdirectly to the cold air streams. Finally, the cooling can be effectedexclusively by a flow of cold water directly impacting the side surface12a of the pipe and adjusted so that the cold water is conveyed over to,and also effectively cools, the side surface of the pipe.

Conveniently, the water which is used in the cooling operation can becollected at the bottom of the jacket 16 and led away from the lattervia a pipe.

After the effected cooling the chamber is withdrawn and the bent pipescan be stored directly or, if desired, put aside for further cooling inair before being stored.

In order to prevent the concave side of the pipe 12 for curling duringthe bending operation, the results of practical tests would seem tosuggest that if heating is carried out in the bending zone in a more orless arbitrary fashion, the compression stresses to which the concaveside is subjected will be at a minimum provided that the pipe is exposedto an additional tensile stress. Alternatively, heating the pipe in thecontrolled manner described in the above embodiments, that is to say bysubjecting the convex side to the maximum and the concave side to theminimum heat, leads to a stiffening or bracing of the concave sidewithout extra tensile stresses having to be utilized. As a practicalmatter, both approaches can be easily combined to a lesser or greaterdegree. It will be appreciated, however, that conditions may varysomewhat all according to the choice of wall thickness, diameter andmaterial for the pipe.

Even if it is not shown in detail in the specification and drawings, itwill be understood that the heating, bending and cooling of the bentpipe can be carried out by an automatically controlled process byemploying suitable control means known per se, and that several bendingapparatus can be coupled together and operated simultaneously.

What I claim is:

1. Apparatus for bending thermoplastic pipes which is capable offunctioning as a self-contained unit and which comprises heat-transfermeans for controllably heating and cooling such a pipe,

means for locating one end of the pipe in a fixed position externally ofsaid heat-transfer means,

means for internally reinforcing the pipe including an inflatablecontainer adapted to be lowered into the pipe and to be inflated to apressure sufficient to cause said container to abut the pipe so as toprovide a reinforcement therefor while suspended therein and means forlowering and raising said container into and out of the pipe when saidcontainer is in its normal deflated condition, and means for applying abending force to said pipe while said pipe is received in saidheat-transfer means with said one end in said fixed position, theheat-transfer means being adapted to pivot as the pipe is being bent byactuation of the bending force-applying means.

2. The apparatus according to claim 1, which also comprises means forapplying direct heat to the internal walls of the pipe.

3. The apparatus according to claim 1, wherein the inflatable containeris weight-loaded.

4. Apparatus for bending thermoplastic pipes which is capable offunctioning as a self-contained unit and which comprises a heat transfermeans for controllably heating and cooling such a pipe, said meansincluding a jacket of substantially U-shaped cross-section adapted tosurround, while spaced from, pipe to form internal heat-transfermedium-conveying surface and nozzles fixed at the base of the U-shapedjacket for supplying heat-transfer medium to be directed at the pipe andto be led by said surfaces to effect the controlled heating and coolingof the pipe, said internal heat-transfer medium-conveying surfacesdefining with the pipe narrow gaps at a transition zone intermediate oneside portion of the pipe facing said nozzles and another side portionfacing away from said nozzles, said internal surfaces projecting freelyoutwards a distance beyond said another side portion to form a whirlchamber immediately adjacent the latter,

means for locating one end of the pipe in a fixed position externally ofsaid heat-transfer means, and means for internally reinforcing the pipeand means for applying a bending force thereto while said pipe isreceived in said heat-transfer means with said one end in said fixedposition, the heat-transfer means being adapted to pivot as the pipe isbeing bent by actuation of the bending forceapplying means.

5. Apparatus for bending thermoplastic pipes which is capable offunctioning as a self-contained unit and which comprises heat-transfermeans for controllably heating and cooling such a pipe,

means for locating one end of the pipe in a fixed position externally ofsaid heat-transfer means, said latter means including a holder to whichthe upper end of the pipe can be secured and from which said pipe canthen be freely suspended downwards substantially vertically, and

means for internally reinforcing the pipe and means for applying abending force thereto while said pipe is received in said heat-transfermeans with said one end in said fixed position, the heat-transfer meansbeing adapted to pivot as the pipe is being bent by actuation of thebending forceapplying means.

6. The apparatus according to claim 5, wherein the means for internallyreinforcing the pipe comprises an inflatable container adapted to beinserted in the lower end of the pipe and to be inflated to a pressuresufficient to cause said container to abut the pipe so as to provide aclosing off means for the pipe end and said closed-off pipe havingfiller material deposited therein.

7. The apparatus according to claim 6, wherein the tiller material ispreheated.

8. Apparatus for bending thermoplastic pipes which is capable offunctioning as a self-contained unit and which comprises a holder forlocating the pipe in a fixed position;

means for internally reinforcing the pipe; means for applying a bendingforce to the pipe while a major portion of the pipe is in heatedcondition; and

means for heating and cooling said pipe portion with regulatabledifferentiated contacting effect along the circumference surface of thepipe; said heating and cooling means comprising a jacket ofsubstantially U-shaped cross-section of sufficient dimension to enclosetherein, while spaced therefrom, said major portions of the pipe inunbent as well as in partly and completely bent condition,

nozzles located at the base of the U-shaped jacket to direct a flow ofheat-transfer medium onto and around the circumference surface of thepipe,

whereas the legs of the U-shaped jacket forms internal heat-transfermedium conveying surfaces to convey the flow of medium from said nozzlesonto and past the pipe surface, and

means for regulating the speed of the heat-transfer medium-flow fromsaid nozzles to involve a regulatable contacting surface of themedium-flow on the pipe surface and thus enabling a correspondingdifferentiated heat-transfer effect on said pipe surface.

9. Apparatus as set forth in claim 8 wherein said means for heating andcooling is pivotably mounted to pivot as the pipe is being bent uponactuation of said means for applying a bending force.

10. Apparatus as set forth in claim 8 wherein said holder is located atone end of the pipe and externally of said means for heating andcooling.

11. Apparatus as set forth in claim 8 wherein said conveying surfacesdefine narrow gaps with the pipe at a transition zone intermediate oneside portion of the pipe facing said nozzles and another side portionfacing away from said nozzles.

12. The apparatus according to claim 8, which comprises means forinternally reinforcing the pipe in the form of an inflatable containerfor inflation in the lower end of the pipe to seal off said lower end,together with a filling composition for introduction in the sealed-offpipe.

13. The apparatus according to claim 12, wherein the filling compositionof the reinforcing means comprises 1 1 material having a specificgravity which is high relative to that of the thermoplastic material ofthe pipe.

14. The apparatus according to claim 12, wherein the filling compositionis in a preheated condition.

15. Apparatus for bending thermoplastic pipes which is capable offunctioning as a self-contained unit and which comprises an upstandingsupport column, a holder fixed thereto for locating one end of the pipeand from which the pipe is suspended downwards in a substantiallyvertical position, heat-transfer means pivotally mounted on said holderbelow said one end of the pipe and for reception of the latter, anabutment member of preselected curvature mounted on said holder andserving as a top for one side portion of the pipe during bendingthereof, means for pivoting the heat-transfer means to cause the pipe tobear against the abutment member, means for internally reinforcing thepipe, said heat-transfer means having nozzles for the regulatable supplyof pressurised heat-transfer medium and said nozzles being arranged tobe directed at a side portion of the pipe opposite said one sideportion, internal walls of said heat-transfer means defining one chamberwith said opposite side portion of the pipe and a whirl chamber havingaccess to the open air with said one side portion of the pipe as well asdefining narrow gaps with portions of the pipe separating said one andsaid opposite side portions, said gaps providing communication betweenthe chambers and the internal construction of the heat-transfer meansbeing such that by regulation of the pressure and heat content of theheat-transfer medium supplied through the nozzles a temperaturedifferential can be produced between the mutually opposite side portionsof the pipe with said opposite side portion being exposed to a moreintense heat than said one side portion of the pipe.

16. The apparatus according to claim 14, which comprises means forinternally heating the pipe pivotably mounted on the support columnabove the holder thereby enabling said means to be swung away from thepipe when not in use.

17. The apparatus according to claim 15, which comprises an inflatablecontainer adapted to be lowered into the pipe and to be inflated to apressure sufficient to cause said container to abut the pipe so as toprovide a reinforcement therefor while suspended therein and means forlowering and raising said container into and out of the pipe when saidcontainer is in its normal deflated condition.

18. The apparatus according to claim 17, wherein the inflatablecontainer is weight-loaded.

19. The apparatus according to claim 15, which comprises means forinternally reinforcing the pipe in the form of an inflatable containerfor inflation in the lower end of the pipe to seal off said lower end,together with a filling composition for introduction in the sealed-off12 pipe.

20. The apparatus according to claim 19, wherein the filling compositionof the reinforcing means comprises material having a specific gravitywhich is high relative to that of the thermoplastic material of thepipe.

21. The apparatus according to claim 19, wherein the filling compositionis in a preheated condition.

22. Apparatus for bending thermoplastic pipes which is capable offunctioning as a self-contained unit and which comprises an upstandingcolumn, a holder fixed thereto of C-shaped horizontal section permittinglateral location of one end of the pipe while the latter is suspendeddownwards in a substantially vertical position, heat-transfer means forreceiving a major portion of the pipe mounted on said holder below saidone end of the pipe and arranged to pivot about a horizontal axis, acurved abutment member mounted on said holder with a substantiallyco'nvex surface facing the pipe, said member serving as a stop for oneside portion of the pipe during bending of the latter, means located atthe base of the heat-transfer means for pivoting the latter and forcausing, as a result of the bending forces, the pipe to bear against theabutment member, means for internally reinforcing the pipe, saidheat-transfer means giving regulatable nozzles directed towards a sideportion of the pipe opposite said one side portion, said nozzles beingarranged vertically one above the other for the supply of pressurisedfluid medium to effect appropriate heating and cooling of the pipe andfurther said heat-transfer means being formed with internal wallsextending substantially at right angles to the longitudinal axis of thepipe and for guiding the pressurised fluid medium partially around thepipe and on to the outside air, said walls defining with said pipe oneither side thereof first and second chambers adjacent and remote fromthe nozzles respectively as well as narrow gaps providing communicationbetween said chambers, the internal design of the heat-transfer meansbeing such that on increasing the pressure of hot pressurised fluidmedium the nozzle-facing side portion of the pipe is exposed to intenseheat which is accompanied by an increasing rate of flow of said hotmedium through said gaps thereby increasing a whirl effect in saidsecond chamber and reducing the heating of said one side portion of thepipe.

23. The apparatus according to claim 22, wherein one of the internalwalls of the heat-transfer means has a portion pivoted about a verticalaxis at a position immediately adjacent the side portion of the pipefacing the nozzles and with respect to the remainder of said wall, saidpivotable wall portion enabling simultaneous lateral location of thepipe in the C-shaped holder and the heat-transfer means.

1. Apparatus for bending thermoplastic pipes which is capable offunctioning as a self-contained unit and which comprises heat-transfermeans for controllably heating and cooling such a pipe, means forlocating one end of the pipe in a fixed position externally of saidheat-transfer means, means for internally reinforcing the pipe includingan inflatable container adapted to be lowered into the pipe and to beinflated to a pressure sufficient to cause said container to abut thepipe so as to provide a reinforcement therefor while suspended thereinand means for lowering and raising said container into and out of thepipe when said container is in its normal deflated condition, and meansfor applying a bending force to said pipe while said pipe is received insaid heattransfer means with said one end in said fixed position, theheat-transfer means being adapted to pivot as the pipe is being bent byactuation of the bending force-applying means.
 2. The apparatusaccording to claim 1, which also comprises means for applying directheat to the internal walls of the pipe.
 3. The apparatus according toclaim 1, wherein the inflatable container is weight-loaded.
 4. Apparatusfor bending thermoplastic pipes which is capable of functioning as aself-contained unit and which comprises a heat transfer means forcontrollably heating and cooling such a pipe, said means including ajacket of substantially U-shaped cross-section adapted to surround,while spaced from, pipe to form internal heat-transfer medium-conveyingsurface and nozzles fixed at the base of the U-shaped jacket forsupplying heat-transfer medium to be directed at the pipe and to be ledby said surfaces to effect the controlled heating and cooling of thepipe, said internal heat-transfer medium-conveying surfaces definingwith the pipe narrow gaps at a transition zone intermediate one sideportion of the pipe facing said nozzles and another side portion facingaway from said nozzles, said internal surfaces projecting freelyoutwards a distance beyond said another side portion to form a whirlchamber immediately adjacent the latter, means for locating one end ofthe pipe in a fixed position externally of said heat-transfer means, andmeans for internally reinforcing the pipe and means for applying abending force thereto while said pipe is received in said heat-transfermeans with said one end in said fixed position, the heat-transfer meansbeing adaPted to pivot as the pipe is being bent by actuation of thebending force-applying means.
 5. Apparatus for bending thermoplasticpipes which is capable of functioning as a self-contained unit and whichcomprises heat-transfer means for controllably heating and cooling sucha pipe, means for locating one end of the pipe in a fixed positionexternally of said heat-transfer means, said latter means including aholder to which the upper end of the pipe can be secured and from whichsaid pipe can then be freely suspended downwards substantiallyvertically, and means for internally reinforcing the pipe and means forapplying a bending force thereto while said pipe is received in saidheat-transfer means with said one end in said fixed position, theheat-transfer means being adapted to pivot as the pipe is being bent byactuation of the bending force-applying means.
 6. The apparatusaccording to claim 5, wherein the means for internally reinforcing thepipe comprises an inflatable container adapted to be inserted in thelower end of the pipe and to be inflated to a pressure sufficient tocause said container to abut the pipe so as to provide a closing offmeans for the pipe end and said closed-off pipe having filler materialdeposited therein.
 7. The apparatus according to claim 6, wherein thefiller material is preheated.
 8. Apparatus for bending thermoplasticpipes which is capable of functioning as a self-contained unit and whichcomprises a holder for locating the pipe in a fixed position; means forinternally reinforcing the pipe; means for applying a bending force tothe pipe while a major portion of the pipe is in heated condition; andmeans for heating and cooling said pipe portion with regulatabledifferentiated contacting effect along the circumference surface of thepipe; said heating and cooling means comprising a jacket ofsubstantially U-shaped cross-section of sufficient dimension to enclosetherein, while spaced therefrom, said major portions of the pipe inunbent as well as in partly and completely bent condition, nozzleslocated at the base of the U-shaped jacket to direct a flow ofheat-transfer medium onto and around the circumference surface of thepipe, whereas the legs of the U-shaped jacket forms internalheat-transfer medium conveying surfaces to convey the flow of mediumfrom said nozzles onto and past the pipe surface, and means forregulating the speed of the heat-transfer medium-flow from said nozzlesto involve a regulatable contacting surface of the medium-flow on thepipe surface and thus enabling a corresponding differentiatedheat-transfer effect on said pipe surface.
 9. Apparatus as set forth inclaim 8 wherein said means for heating and cooling is pivotably mountedto pivot as the pipe is being bent upon actuation of said means forapplying a bending force.
 10. Apparatus as set forth in claim 8 whereinsaid holder is located at one end of the pipe and externally of saidmeans for heating and cooling.
 11. Apparatus as set forth in claim 8wherein said conveying surfaces define narrow gaps with the pipe at atransition zone intermediate one side portion of the pipe facing saidnozzles and another side portion facing away from said nozzles.
 12. Theapparatus according to claim 8, which comprises means for internallyreinforcing the pipe in the form of an inflatable container forinflation in the lower end of the pipe to seal off said lower end,together with a filling composition for introduction in the sealed-offpipe.
 13. The apparatus according to claim 12, wherein the fillingcomposition of the reinforcing means comprises material having aspecific gravity which is high relative to that of the thermoplasticmaterial of the pipe.
 14. The apparatus according to claim 12, whereinthe filling composition is in a preheated condition.
 15. Apparatus forbending thermoplastic pipes which is capable of functioning as aself-contained unit and Which comprises an upstanding support column, aholder fixed thereto for locating one end of the pipe and from which thepipe is suspended downwards in a substantially vertical position,heat-transfer means pivotally mounted on said holder below said one endof the pipe and for reception of the latter, an abutment member ofpreselected curvature mounted on said holder and serving as a top forone side portion of the pipe during bending thereof, means for pivotingthe heat-transfer means to cause the pipe to bear against the abutmentmember, means for internally reinforcing the pipe, said heat-transfermeans having nozzles for the regulatable supply of pressurisedheat-transfer medium and said nozzles being arranged to be directed at aside portion of the pipe opposite said one side portion, internal wallsof said heat-transfer means defining one chamber with said opposite sideportion of the pipe and a whirl chamber having access to the open airwith said one side portion of the pipe as well as defining narrow gapswith portions of the pipe separating said one and said opposite sideportions, said gaps providing communication between the chambers and theinternal construction of the heat-transfer means being such that byregulation of the pressure and heat content of the heat-transfer mediumsupplied through the nozzles a temperature differential can be producedbetween the mutually opposite side portions of the pipe with saidopposite side portion being exposed to a more intense heat than said oneside portion of the pipe.
 16. The apparatus according to claim 14, whichcomprises means for internally heating the pipe pivotably mounted on thesupport column above the holder thereby enabling said means to be swungaway from the pipe when not in use.
 17. The apparatus according to claim15, which comprises an inflatable container adapted to be lowered intothe pipe and to be inflated to a pressure sufficient to cause saidcontainer to abut the pipe so as to provide a reinforcement thereforwhile suspended therein and means for lowering and raising saidcontainer into and out of the pipe when said container is in its normaldeflated condition.
 18. The apparatus according to claim 17, wherein theinflatable container is weight-loaded.
 19. The apparatus according toclaim 15, which comprises means for internally reinforcing the pipe inthe form of an inflatable container for inflation in the lower end ofthe pipe to seal off said lower end, together with a filling compositionfor introduction in the sealed-off pipe.
 20. The apparatus according toclaim 19, wherein the filling composition of the reinforcing meanscomprises material having a specific gravity which is high relative tothat of the thermoplastic material of the pipe.
 21. The apparatusaccording to claim 19, wherein the filling composition is in a preheatedcondition.
 22. Apparatus for bending thermoplastic pipes which iscapable of functioning as a self-contained unit and which comprises anupstanding column, a holder fixed thereto of C-shaped horizontal sectionpermitting lateral location of one end of the pipe while the latter issuspended downwards in a substantially vertical position, heat-transfermeans for receiving a major portion of the pipe mounted on said holderbelow said one end of the pipe and arranged to pivot about a horizontalaxis, a curved abutment member mounted on said holder with asubstantially convex surface facing the pipe, said member serving as astop for one side portion of the pipe during bending of the latter,means located at the base of the heat-transfer means for pivoting thelatter and for causing, as a result of the bending forces, the pipe tobear against the abutment member, means for internally reinforcing thepipe, said heat-transfer means giving regulatable nozzles directedtowards a side portion of the pipe opposite said one side portion, saidnozzles being arranged vertically one above the other for the supply ofpressurised fluid medium to effect appropriate heaTing and cooling ofthe pipe and further said heat-transfer means being formed with internalwalls extending substantially at right angles to the longitudinal axisof the pipe and for guiding the pressurised fluid medium partiallyaround the pipe and on to the outside air, said walls defining with saidpipe on either side thereof first and second chambers adjacent andremote from the nozzles respectively as well as narrow gaps providingcommunication between said chambers, the internal design of theheat-transfer means being such that on increasing the pressure of hotpressurised fluid medium the nozzle-facing side portion of the pipe isexposed to intense heat which is accompanied by an increasing rate offlow of said hot medium through said gaps thereby increasing a whirleffect in said second chamber and reducing the heating of said one sideportion of the pipe.
 23. The apparatus according to claim 22, whereinone of the internal walls of the heat-transfer means has a portionpivoted about a vertical axis at a position immediately adjacent theside portion of the pipe facing the nozzles and with respect to theremainder of said wall, said pivotable wall portion enablingsimultaneous lateral location of the pipe in the C-shaped holder and theheat-transfer means.